In an active-matrix display device such as a liquid crystal display device or an organic electroluminescence (EL) display device, thin-film transistors, which are also known as the TFTs are used.
In such a display device, thin-film transistors are arranged in an array to constitute a thin-film transistor array device. In each pixel, a driver transistor for driving the pixel and a switching transistor for selecting the pixel are formed.
In particular, in a light-emitting organic EL display device having organic EL elements, different capacity is required for the driving transistor and the switching transistor. More specifically, satisfactory turn-on characteristics are required for the driving transistor in order to improve the driving capacity of the organic EL element, while satisfactory turn-off characteristics are required for the switching transistor.
As an example of such a technique, the patent literature 1 discloses an organic EL display device in which two types of thin film transistors having different characteristics are provided in one pixel. In the patent literature 1, two types of transistors having different characteristics are formed in one pixel by having different crystalline property in the channel layers for the driving transistor and the switching transistor.